实际上,我可以使用img.onload
函数来完成它。这是我从 'HTML5画布-如何在图像背景上绘制线条?'学到的方法。但我需要在不使用img
和onload
函数的情况下绘制图像,方法如下:
var imagePaper = new Image();
imagePaper.onload = function(){
context.drawImage(imagePaper,100, 20, 500,500);
};
imagePaper.src = "images/main_timerand3papers.png";
}
但我希望能够简单地在画布上方附加img src并绘制矩形,就像这样:
<body>
<img id="scream" src="my.jpg" alt="The Scream" width="220" height="277">
<p>Canvas:</p>
<canvas id="myCanvas" width="500" height="500" >
Your browser does not support the HTML5 canvas tag.</canvas>
但是我无法在canvas上绘制图像之上的线条,无论是图像先绘制还是形状被遮挡。这是我的完整代码:
<!DOCTYPE html>
<head>
<title>Playing YouTube video on HTML5 canvas</title>
<meta name="viewport" content="user-scalable=no, initial-scale=1.0, maximum-scale=1.0, width=device-width" />
<style type="text/css">
body {
margin: 0px;
padding: 0px;
}
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
</head>
<body>
<img id="scream" src="my.jpg" alt="The Scream" width="220" height="277">
<p>Canvas:</p>
<canvas id="myCanvas" width="500" height="500" >
Your browser does not support the HTML5 canvas tag.</canvas>
<script>
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var img=document.getElementById("scream");
ctx.drawImage(img,10,10);
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
context.beginPath();
context.rect(188, 50, 200, 100);
context.fillStyle = 'yellow';
context.fill();
context.lineWidth = 7;
context.strokeStyle = 'black';
context.stroke();
</script>
</body>
</html>
position: absolute
样式,这样它就可以直接放在<img>
上面,而且不需要把图片绘制到画布中 - 也就是只使用组合。 - Alnitak